The present invention relates to an interface circuit for a display device such as a CRT (Cathode Ray Tube), or more particularly to an interface circuit capable of minimizing the video RAM dead area to display as much data as possible at a time without changing the video RAM capacity.
In the reverse display on a CRT, characters displayed closest to the screen edge are illegible because they overlap "margin a" surrounding the CRT screen as shown in FIG. 7.
The conventional solution to this problem is to set dead area b where no character is displayed in the vicinity of the "margin a" (see FIG. 8). The dead area b setting has been achieved by programming.
With this conventional display method, however a, smaller video RAM capacity is used for data display than the allocated hardware capacity for data display. In other words, dead area results in the video RAM; the video RAM cannot be used to the maximum capacity to display as much volume of data as possible.